ALCOHOL ADDUCTS OF ALKOXIDES - INTRAMOLECULAR HYDROGEN-BONDING AS A GENERAL STRUCTURAL FEATURE

Characterization of Zr2(OiPr)8(iPrOH)2 by 1H and 13C NMR spectroscopy, IR spectroscopy, and single-crystal X-ray diffraction (-100 °C) is reported. The compound crystallizes in the space group [formula omited] with a = 18.262 (4) Å, b= 19.883 (5) Å, c = 12.067 (3) Å, α = 98.59 (1)°, β = 96.26 (1)°, γ = 77.49 (1)°, and Z = 4. The unit cell contains four half-dimers in the asymmetric unit, all of which differ only in the rotational conformation about Zr-O and O-C bonds. In each dimer, the edge-shared bioctahedron has two μ-OiPr groups. On opposite sides of this Zr2(μ-OR)2 plane, each dimer forms two hydrogen bonds, one each between a coordinated alcohol and a terminal alkoxide. The NMR spectra at 25 °C are so simple as to be structurally uninformative, a result of rapid fluxionality which includes, as one component, proton migration among all OiPr units. At -80 °C in toluene, the NMR spectra are now too complex to be accounted for by a single edge-shared bioctahedral structure. The hafnium analogue is isomorphous with the zirconium compound. Although Ce2(OiPr)g(iPrOH)2 is not isomorphous, it exhibits an analogous hydrogen-bonded structure in which the O⋯O distance is as short as it is in the Zr analogue, in spite of a metal-metal separation which is longer by 0.28 Å. It crystallizes in the space group [formula omited] with a = 11.385 (4) Å, b = 12.144 (5) Å, c = 9.009 (3) Å, α = 109.72 (1)°, β = 111.54 (2)°, γ = 65.70 (1)°, and Z = 1. The generality of hydrogen bonding between M-OR and M-O(H)R groups when they are aligned parallel in a metal cluster is reviewed. © 1990, American Chemical Society. All rights reserved.